Republican presidential candidates, from left, former Massachusetts Gov. Mitt Romney, Texas Gov. Rick Perry, Rep. Ron Paul (Texas), businessman Herman Cain and former Utah Gov. Jon Huntsman.(AP Photo/Chris Carlson) (Chris Carlson/AP)

Here are five key things to look for in tonight’s debate:

1. Is Herman Cain a contender or a pretender? In previous debates, Cain was the genial candidate-without-a-prayer on the very end of the stage, talking up his 9-9-9 tax plan and his preference for the Chilean model of social security. Tuesday night, because of his rapid rise in national polls, the former Godfather’s Pizza CEO will have Mitt Romney to his left and Texas Governor Rick Perry to his right.

So how do they treat him when he is at their elbows and nipping at their heels in polls?

Romney has praised Cain’s business background, suggesting that he doesn’t see Cain as a threat. In fact, Cain’s continued presence and strong showing only help Romney. Perry, on the other hand, has the most to gain by going after Cain. But he must weigh whether tangling with Cain is actually punching down.

Regardless of whether he is attacked, to sustain his rise, Cain must get more specific about his economic plan, and show that he is more than a flash- in-the-pan candidate with a catchy slogan.

2. Can Romney take a punch? Romney has come out of every debate with hardly a hair out of place, able to keep focused on his anti-Obama message, and deflect and dismiss his rivals with a simple turn of phrase.

With New Hampshire polls showing Romney with a strong lead, and national polls also indicating that he is at the top of the field and considered strong on the economy, the six men and one woman sitting around the table tonight could see a pile-on-Romney moment.

And there’s no better opportunity to try to knock Romney off his front-runner stride than over the economy, his perceived strength. He has yet to face sustained criticism for his record in the private sector or as governor of Massachusetts. With possible attacks coming from all sides, it will be difficult to ignore everyone. Romney will have to have more than a “nice try” response at the ready to defend himself.

3. Rick Perry rebound? Perry’s individual debate performances have been very much like the trajectory of his candidacy so far: he starts strong, then fades down the stretch. His Saturday Night Live-worthy showing in the last debate triggered his downward spiral in the polls, and his statements on military intervention in Mexico and the revelations about his family’s hunting camp further damaged him.

While it’s true that many voters haven’t begun to tune in to the debates (available for your viewing pleasure tonight on and on Bloomberg TV), party bigwigs are paying attention. They are looking for a reason to either give the $17 million man another chance, or write him off as not sharp enough for the job.

In Florida, Perry seemed like the kid who crammed the night before and had memorized most of the material, but didn’t really know it. Over the last few days, his team has set up a debate study hall complete with a faux Romney to spar with. Aides also ordered Perry to get more sleep. With three debates behind him, he knows what’s coming — jobs, taxes, immigration, health care etc. He has to act steady, confident, prepared, and comfortable tonight--or risk a sustained slide.

4. Will the debate veer off topic? Although debates are among the most planned, haggled-over events of a campaign season, they are also the most unpredictable. The format of this debate will be tighter than previous ones, with a focus on the economy. Yet, much has happened on the stump since the last debate that has nothing to do with the candidates’ economic plans.

In the week leading up to the debate, two crucial things happened. First, there was the revelation of a Perry family hunting camp with a racially charged name. Second, a Perry supporter called Mormonism a cult, a charge that Perry disavowed. Yes, the debate is supposed to be about the economy, but with two Mormons — Romney and Jon Huntsman — and a black man (Cain) around the table, can the moderators and candidates avoid talking about race and religion? Or will there be a clear-the-air moment? Whatever happens tonight, with a black president in the White House, and a black conservative and a Mormon front-runner in the Republican contest, race and religion are sure remain hot-button issues.

5. Who will debate his or her way into a Saturday Night Live skit? Admit it. Part of the appeal of watching presidential candidates debate each other is looking for a misstep or odd moment that leads straight to the writing table of the SNL cast.

Did George W. Bush really use the word “strategery” to sum up his candidacy or was that Will Ferrell? And did Sarah Palin really ask Joe Biden in a debate, “Can I call you Joe?” Or was that Tina Fey? The point is that Saturday Night Live has a knack for framing candidates and all their tics and weaknesses early on, in a way that isn’t easy to shake.

While Alec Baldwin’s take on Rick Perry’s debate performance missed the mark on Perry’s accent (it was more Mississippi than Texas), Baldwin nailed Perry’s sleepwalker approach to attacking Romney. Baldwin could have skipped the yawn and the falling asleep at the podium, and simply read what Perry said, and still scored big laughs. It shouldn’t be that easy.